Oscillatory circuit for ultrasonic cleaning apparatus

ABSTRACT

A high-efficient oscillatory circuit drives a piezoelectric crystal (transducer) which is coupled to an ultrasonic cleaning tank. The circuit includes a transistor switching means in the driver side of the oscillator. The primary winding of the transformer is coupled in parallel with a capacitor and forms a circuit having a resonant frequency which is a multiple even integer of the resonant frequency of the crystal which is coupled to the transformer secondary winding.

United States Patent UNITED STATES PATENTS 11/1967 Branson ..259/l XPuskas Mar. 21, 1972 [54] OSCILLATORY CIRCUIT FOR 3,152,295 10 1964Schebler ..310/s.1 x ULTRASONIC CLEANING APPARATUS 3,575,383 4/19710616mm... ..259 72 2,967,957 l/l961 Massa.... BIO/8.5 X [72] Inventor:Wllllam L. Puskas, Trumbull, Conn. 2 271 200 1 1942 Mason 3 0 2 x 73 Asne B mo Inst 8 ts 1 co r M St 3,256,498 6/1966 Hurtig.... 331/155 x 1 eform, Com, rum n a am 3,432,691 3/1969 ShOll ..310/s 1 [22] Filed: Dec.10, 1970 Primary Examiner-J. D. Miller Assistant ExaminerB. A. Reynolds[2]] Appl' Attorney-Ervin B.Steinberg [52] US. Cl. ..310/8.l, 259/1 R,3l0/8.7, [57] ABSTRACT [51] lm Cl A high-efficient oscillatory circuitdrives a piezoelectric 58 Fieid 259 7 crystal (transducer) which iscoupled to an ultrasonic cleaning 259/72 33 l 16 158 5 1 tank. Thecircuit includes a transistor switching means in the 130 driver side ofthe oscillator. The primary winding of the transformer is coupled inparallel with a capacitor and forms a cir- 56] References Cited cuithaving a resonant frequency which is a multiple even integer of theresonant frequency of the crystal which is coupled to the transformersecondary winding.

15 Claims, 4 Drawing Figures PAIENTEUMARZI 1912 v 3mm 1 BF 2 III WILLIAML. PUSKAS INVENTOR.

PATENTEU ARZI I9 2 3,651,352

SHEET 2 [1F 2 F G. 3 TRANSISTOR SWITCHING STATE ON OFF .i

VOLTAGE I I B-A VOLTAGE ACROSS TRANSFORMER 0 SECONDARY- TIM E WILLIAM L.PUSKAS INVENTOR.

OSCILLATORY CIRCUIT FOR ULTRASONIC CLEANING APPARATUS The presentinvention refers to an oscillatory circuit for an ultrasonic cleaningapparatus and, more specifically, has reference to a simplifiedelectronic circuit for driving an ultrasonic cleaning apparatus,particularly, an ultrasonic cleaning apparatus of the smaller type asused, for instance, in the laboratory, jewelry repair shops, homeworkshop, and the like.

The electrical circuit disclosed hereafter is characterized, quitespecifically, by a high degree of efficiency, high reliability, byrelatively few components and is, therefore, relatively simple andinexpensive as is a necessity when providing ultrasonic cleaningapparatus of the type indicated heretofore. Moreover, the highefficiency obtained is the result of a unique and novel circuitarrangement which provides for the conservation of stored energy.

The above indicated characteristics and advantages will be more clearlyapparent from the following detailed description when considered inconjunction with the accompanying drawings, in which:

FIG. 1 is a schematic illustration of the ultrasonic cleaning apparatus;

FIG. 2 is a schematic diagram of an electrical circuit employedembodying the present invention;

FIG. 3 is a schematic diagram of the wave shapes at certain points inFIG. 2, and

FIG. 4 is a schematic electrical circuit diagram of a further embodimentof the present invention.

Referring now to the figures, and FIG. 1 in particular, there is shown askirt or enclosure 12 which supports therein a metal tank 14 which isfilled with a cleaning liquid 16. The skirt l2 rests on a base 18 whichis provided with a set of rubber feet 20.

A piezoelectric crystal 22, also called transducer, preferably ofdisk-shape, is bonded by means of a layer of epoxy resin material 24 tothe underside of the tank 14 for imparting ultrasonic energy to the tankand to the cleaning liquid 16 in a manner that is well understood bythose skilled in the art. The crystal 22 is connected by conductors 26to an electronic circuit 28 which, in turn, by a power cord 30 can beconnected to a standard 1 volts AC, 60-cycle, power line.

The cleaning tank and the piezoelectric crystal attached thereto maytake the form as shown for instance in U.S. Pat. No. 3,516,645 datedJune 23, 1970 issued to J. P. Arndt et al., entitled Ultrasonic Cleaner.

The novel, high-efficient and simple electronic circuit for setting thecrystal 22 into resonance is shown in FIG. 2. The AC terminals 32 and 34apply electrical power to a bridgetype rectifier 36 which is connectedto a filter capacitor 38 in order to provide direct current energy. Atransformer 40, preferably having a toroidal core, has a primary winding42, a secondary winding 44, and a feedback winding 46. The primarywinding 42 is coupled in parallel with a capacitor 43 and this parallelcombination, forming an oscillatory circuit, is connected to a switchingtransistor 50 which is cyclically rendered conductive by the signalprovided by the feedback winding 46. The capacitor 48 provides phaseshift correction and the resistor 49, rectifier 52 and resistor 66provide the normal biasing potential.

The piezoelectric crystal 22 is connected in parallel with an inductance54 to the secondary transformer winding 44 and, thus, the crystal 22,inductance 54 and winding 44 form a parallel resonant circuit, causingthe crystal to oscillate and impart the ultrasonic energy to thecleaning liquid. In a typical example, the crystal is selected to have anatural resonant frequency in the range from 40 to 60 kHz. It should beunderstood, however, that this frequency range is merely illustrative ofa typical operating condition and that other frequencies may be used aswell.

The driving portion of the circuit, that is the primary winding 42, thecapacitor 43 and the reflected reactance, form an oscillatory circuitand the capacitor 43 is selected to cause the resonant frequency of thiscombination to be an even integer multiple of the resonant frequency ofthe transducer or crystal 22. In a typical example, the resonantfrequency of the driving portion is four times that of the parallelresonant circuit which includes the piezoelectric crystal 22. Therefore,if the crystal is driven at its resonant frequency of, let us say 45kHz., the primary side is tuned to exhibit a frequency of kHz.

FIG. 3 shows the typical wave shapes which occur in the circuit per FIG.2. The line 60 shows the transistor 50 being cyclically switched andwhenrendered conductive at time I, providing current flow from the DCpower supply through the primary winding 42 and transistor 50 to ground.As the current conduction through the transistor ceases, time t thevoltage across the capacitor 43 rises, voltage B-A, and the winding 42together with the capacitor 43 and the reflected reactance of the othercircuit components form an oscillatory circuit which has a fundamentalfrequency of four times the frequency of the oscillatory load circuitportion which includesthe transducer 22.

The salient advantage of the present arrangement is seen at the time t,when the transistor is rendered conductive. The voltage across theprimary transformer winding points B-A has reached a low state in itsoscillation. As a result thereof, there is a minimum amount of energystored in the resonant circuit. At this particular moment only thisminimum amount of energy is conducted to ground by the transistor 50.Further, during the time interval in which the transistor isnonconductive, the high-frequency oscillation across the primary windingof the transformer is transferred to the load. These phenomena result,of course, in a higher degree of efficiency than the heretofore usedcircuits.

One further advantage of the present invention resides in the fact thetransformer 40, on account of the frequency on the primary side of thecircuit being higher than the frequency determined by the resonance ofthe crystal 22, can be made smaller and, therefore, is lighter and lessexpensive. Last but not least, since the electric energy stored is aminimum at the time the transistor is rendered conductive, current peaksduring transistor switching are avoided and the transistor reliabilityis greatly improved.

A further improvement is incorporated in the circuit shown in FIG. 4.The circuit shown is identical with that in FIG. 2 except for theaddition of inductance 62 and capacitor 64. The inductance 62 connectedin series with the capacitor 43 delays momentarily the onset of heavycurrent flow through the transistor, permitting the transistor to attainits saturation level before heavy current is conducted therethrough.This arrangement prevents undue power dissipation by the transistor.Energy not dissipated in the transistor remains stored in the capacitor38, thus contributing to greater efficiency. Because of the reducedstress on the transistor, the above circuit has been used successfully,for instance, to drive two transducers 22 with a single transistor 50.

The circuit per FIG. 4 shows a further improvement. A common cause ofcircuit defect is attributable to a failure of the transducer 22 caused,for instance, by cracking of the ceramic disk, conductor lead breakage,etc. When the transducer 22 fails in the circuit per FIG. 2, there nolonger exists a parallel resonant circuit at the output side and, hence,the oscillations cease. Resistor 66 biases the transistor in theconductive condition and the collector current 1 increases until thetransistor 50 is destroyed. The parallel capacitor 64 added in FIG. 4sustains the circuit in a higher frequency oscillatory mode when thetransducer 22 fails. Hence, a transducer failure will no longer resultin an electrical circuit failure.

What is claimed is:

1. An oscillatory circuit for an ultrasonic cleaning apparatuscomprising:

a transformer having a primary winding and a secondary winding;

a capacitance coupled in parallel with said primary winding;

a source of direct current and a switching means coupled serially incircuit with said primary winding and parallelcoupled capacitance forcyclically providing current flow from said source through said winding;

said secondary winding coupled in parallel with an inductance and apiezoelectric element, the latter forming a part of said cleaningapparatus;

a further winding serving as a feedback means disposed on saidtransformer coupled to said switching means to cause said cyclic currentflow, and

the combination of said primary winding and capacitance forming aresonant circuit having a resonant frequency which is an even integermultiple of the frequency of the oscillatory circuit comprising saidsecondary winding, said inductance and piezoelectric element,

2. An oscillatory circuit as set forth in claim 1, said primary windingand capacitance in combination having a resonant frequency which is fourtimes higher than the resonant frequency determined by the oscillatorycircuit comprising said secondary winding, said inductance andpiezoelectric element.

3. An oscillatory circuit as set forth in claim 1, the combination ofsaid secondary winding, said inductance and piezoelectric element beingresonant at a frequency of at least 20 kHz.

4. An oscillatory circuit as set forth in claim 1, said switching meansbeing a transistor.

5. An oscillatory circuit as set forth in claim 1, said piezoelectricelement being a disk-type element coupled to an exterior surface of anultrasonic cleaning tank.

6. An oscillatory circuit as set forth in claim 1, said primary,secondary and further windings being disposed on a toroidal transformercore.

7. An oscillatory circuit for an ultrasonic cleaning apparatus, saidcircuit comprising:

a driving portion which includes a source of direct current,

a switching means, a first transformer winding, and a capacitanceconnected in parallel with said first winding so arranged that saidswitching means is adapted to cyclically provide current flow from saidsource through said winding;

a load portion which includes a second transformer winding inductivelycoupled to said first winding, a piezoelectric transducer, and aninductance coupled to said second winding and to said transducer; and

said driving portion being dimensioned to exhibit when said switchingmeans inhibits current flow from said source to said first winding afundamental resonant frequency which is an even integer multiple of thefundamental frequency ofsaid transducer.

8. An oscillatory circuit for an ultrasonic cleaning apparatuscomprising:

a transformer having a primary winding and a secondary winding;

the series combination of a capacitance and an inductance coupled inparallel with said primary winding;

a source of direct current and a switching means coupled serially incircuit with said primary winding and said parallel coupled seriescombination for cyclically providing current flow from said sourcethrough said winding;

said secondary winding coupled in parallel with an inductance and apiezoelectric element, the latter forming a part of said cleaningapparatus;

a further winding serving as a feedback means disposed on saidtransformer coupled to said switching means to cause said cyclic currentflow, and

the combination of said primary winding and series combination forming aresonant circuit having a resonant frequency which is an even integermultiple of the frequency of the oscillatory circuit comprising saidsecondary winding, said inductance and piezoelectric element.

9. An oscillatory circuit as set forth in claim 8, said primary windingand series combination coupled in parallel in combination having aresonant frequency which is four times higher than the resonantfrequency determined by the oscillatory circuit comprising saidsecondary winding, said inductance and piezoelectric element.

10. An oscillatory circuit as set forth in claim 8, the combination ofsaid secondary winding, said inductance and piezoelectric element beingresonant at a frequency of at least 20 kHz.

11. An oscillatory circuit as set forth in claim 8, said switching meansbeing a transistor.

12. An oscillatory circuit as set forth in claim 8, said piezoelectricelement being a disk-type element coupled to an exterior surface of anultrasonic cleaning tank.

13. An oscillatory circuit as set forth in claim 8, said primary,secondary and further windings being disposed on a toroidal transformercore.

14. An oscillatory circuit as set forth in claim 8, and a capacitancecoupled in parallel with said piezoelectric element.

15. An oscillatory circuit for an ultrasonic cleaning apparatuscomprising:

a driving circuit portion;

an output circuit portion which includes a transducer having apredetermined resonant frequency;

means coupling said portions to each other, and

said driving circuit portion having a combination of circuit elementsadapted to be resonant at a frequency which is an even integer multipleof said predetermined resonant frequency.

1. An oscillatory circuit for an ultrasonic cleaning apparatuscomprising: a transformer having a primary winding and a secondarywinding; a capacitance coupled in parallel with said primary winding; asource of direct current and a switching means coupled serially incircuit with said primary winding and parallelcoupled capacitance forcyclically providing current flow from said source through said winding;said secondary winding coupled in parallel with an inductance and apiezoelectric element, the latter forming a part of said cleaningapparatus; a further winding serving as a feedback means disposed onsaid transformer coupled to said switching means to cause said cycliccurrent flow, and the combination of said primary winding andcapacitance forming a resonant circuit having a resonant frequency whichis an even integer multiple of the frequency of the oscillatory circuitcomprising said secondary winding, said inductance and piezoelectricelement.
 2. An oscillatory circuit as set forth in claim 1, said primarywinding and capacitance in combination having a resonant frequency whichis four times higher than the resonant frequency determined by theoscillatory circuit comprising said secondary winding, said inductanceand piezoelectric element.
 3. An oscillatory circuit as set forth inclaim 1, the combination of said secondary winding, said inductance andpiezoelectric element being resonant at a frequency of at least 20 kHz.4. An oscillatory circuit as set forth in claim 1, said switching meansbeing a transistor.
 5. An oscillatory circuit as set forth in claim 1,said piezoelectric element being a disk-type element coupled to anexterior surface of an ultrasonic cleaning tank.
 6. An oscillatorycircuit as set forth in claim 1, said primary, secondary and furtherwindings being disposed on a toroidal transformer core.
 7. Anoscillatory circuit for an ultrasonic cleaning apparatus, said circuitcomprising: a driving portion which includes a source of direct current,a switching means, a first transformer winding, and a capacitanceconnected in parallel with said first winding so arranged that saidswitching means is adapted to cyclically provide current flow from saidsource through said winding; a load portion which includes a secondtransformer winding inductively coupled to said first winding, apiezoelectric transducer, and an inductance coupled to said secondwinding and to said transducer; and said driving portion beingdimensioned to exhibit when said switching means inhibits current flowfrom said source to said first winding a fundamental resonant frequencywhich is an even integer multiple of the fundamental frequency of saidtransducer.
 8. An oscillatory circuit for an ultrasonic cleaningapparatus coMprising: a transformer having a primary winding and asecondary winding; the series combination of a capacitance and aninductance coupled in parallel with said primary winding; a source ofdirect current and a switching means coupled serially in circuit withsaid primary winding and said parallel coupled series combination forcyclically providing current flow from said source through said winding;said secondary winding coupled in parallel with an inductance and apiezoelectric element, the latter forming a part of said cleaningapparatus; a further winding serving as a feedback means disposed onsaid transformer coupled to said switching means to cause said cycliccurrent flow, and the combination of said primary winding and seriescombination forming a resonant circuit having a resonant frequency whichis an even integer multiple of the frequency of the oscillatory circuitcomprising said secondary winding, said inductance and piezoelectricelement.
 9. An oscillatory circuit as set forth in claim 8, said primarywinding and series combination coupled in parallel in combination havinga resonant frequency which is four times higher than the resonantfrequency determined by the oscillatory circuit comprising saidsecondary winding, said inductance and piezoelectric element.
 10. Anoscillatory circuit as set forth in claim 8, the combination of saidsecondary winding, said inductance and piezoelectric element beingresonant at a frequency of at least 20 kHz.
 11. An oscillatory circuitas set forth in claim 8, said switching means being a transistor.
 12. Anoscillatory circuit as set forth in claim 8, said piezoelectric elementbeing a disk-type element coupled to an exterior surface of anultrasonic cleaning tank.
 13. An oscillatory circuit as set forth inclaim 8, said primary, secondary and further windings being disposed ona toroidal transformer core.
 14. An oscillatory circuit as set forth inclaim 8, and a capacitance coupled in parallel with said piezoelectricelement.
 15. An oscillatory circuit for an ultrasonic cleaning apparatuscomprising: a driving circuit portion; an output circuit portion whichincludes a transducer having a predetermined resonant frequency; meanscoupling said portions to each other, and said driving circuit portionhaving a combination of circuit elements adapted to be resonant at afrequency which is an even integer multiple of said predeterminedresonant frequency.